The Lost Waterbender
by FlyteNyte
Summary: The Fire Nation celebrated its victory over the Avatar cycle when they killed the very last Waterbender. With no host to be reborn into, the Avatar cycle ended. Until 100 years later, when Elsa found that Ahtohallen is more than just memories. Now she must master all four elements if she ever wants to see Arendelle again. Avatar!Elsa. Crossover with ATLA. Post Frozen 2.
1. Prologue

_._

_Every inch of me is trembling_  
_But not from the cold_  
_Something is familiar_  
_Like a dream I can reach but not quite hold_

Crossing the dark sea was exhilarating. Elsa felt the water spirit galloping beneath her and the air whipping around her. She was aware of the elements in ways she had only ever been aware of the ice before, like if she reached just a little further she could guide them too. She had never felt so certain she was making the right choice. Leaving Anna behind had hurt but she could never have survived the water spirit's anger.

Elsa would find the truth about Arendelle, the Northuldra, and about her powers at Ahtohallen. The siren sang on.

_I can sense you there_  
_Like a friend I've always known_  
_I'm arriving_  
_And it feels like I am home_

The glacier at her fingertips hummed with power the way nothing ever had. At first touch, her mind flicked to the strange people she had seen her entire life at the edge of her vision. A tall woman with painted blue arrow tattoos. A man who could spit fire itself. A painted face, clad in armor and surrounded by earth. They were more clear in her mind than the fuzzy glimpses of her childhood. She needed to meet them. They had to be in here.

_I have always been a fortress_  
_Cold secrets deep inside_  
_You have secrets, too_  
_But you don't have to hide_

The ice flowed in her blood. Moved like a frozen river. Elsa was thrown into another vision of bright arrows and wind so strong it could only be Gale's influence. She pressed onward, giddy with power.

_Show yourself_  
_I'm dying to meet you_  
_It's your turn_  
_Are you the one I've been looking for_  
_All of my life?_  
_Show yourself_  
_I'm ready to learn_

The teasing light drew her deeper. Elsa thought back to a moment in childhood that she thinks might be her first memory. When the ice had first responded to her, she had seen a woman with a deep blue furred cloak beside her in the snow. She wore beads covered by the elemental symbols the Northuldra worshipped. It was all connected, it had to be.

_I've never felt so certain_  
_All my life I've been torn_  
_But I'm here for a reason_  
_Could it be the reason I was born?_  
_I have always been so different_  
_Normal rules did not apply_  
_Is this the day?_  
_Are you the way_  
_I finally find out why?_

As the glacier opened up, the ice showed her moving dioramas of people she had never met. Impossible visages, moments lost to time. Anna always said her powers were not a curse, they were a gift. Elsa had never once believed her. Here though in Ahtohallen, surrounded by the memories of her people and ice so old it had witnessed all of history, she almost believed Anna.

She saw her mother's face among the ghostly figures and began to cry.

_Show yourself_  
_I'm no longer trembling_  
_Here I am_  
_I've come so far_  
_You are the answer I've waited for_  
_All of my life_  
_Oh, show yourself_  
_Let me see who you are_

Arendelle's history was laid out now. The truth about the Northuldra, about her grandfather, about the dam. It was more than she could take. She had to get this back to Anna.

But it wasn't _enough_, where was the voice? The people from her dreams?

_Where the north wind meets the sea_  
_There's a river_  
_Full of memory_  
_Come, my darling, homeward bound_  
_I am found_

The air was thinner here, everything had an untethered feel and Elsa knew in the back of her mind she should stop. But they had to be just a little further.

The newest icy figure in front of her stopped her dead in her tracks. Another ice magic user. The moving statue was visibly Northuldra, at least in the face. She threw ice spikes in a brilliant arc out in front of her palms towards a man in unfamiliar armor. His face twisted with anger and he held his odd stance, unafraid of the ice. Walking around them, she saw the female figure was guarding a child. The mystery of the moment was overwhelming.

Before she could puzzle any further, a new statue caught her eye. She turned to see the woman with the arrow tattoos standing tall and still. Her eyes met the statue's own, taking up her entire field of view. It lit up incandescently and made a smooth motion unlike anything Elsa had ever seen before freezing cold air washed over her. In that moment, Elsa felt the truth about her power deep in her very bones. She was the fifth spirit. And something _else._

She had only moments to get a single message to Anna before everything went dark. She had found the voice inside her.

**"Its good to see you, Avatar Elsa. I have been waiting a long time."**

_Step into the power_  
_Grow yourself_  
_Into something new_  
_You are the one you've been waiting for_

_All of my life_

* * *

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_AN/ Plans: __I'm hoping this will be quite long. __Not a shipfic, but there probably will be a F/F love interest eventually. Just a warning for those that consider it a dealbreaker._

_Mainly I want Elsa to enter a world ravaged by a victorious Fire Nation and go on an adventure worthy of the Gaang. Def a fusion fic, as Elsa will interact with canon ATLA characters during this. Shes older than any ATLA character was so situations will be suitably more mature and canon ATLA characters will be aged up to match._

_CONSTRUCTIVE CRITICISM WELCOME. PMs welcome._

_Reviews are my applause._


	2. Into The Unknown

Anna stood at the cliffside overlooking the fjord and held on so tightly to Kristoff she was bruising his arm. He didn't complain. Neither had words to describe what they saw.

Arendelle's destruction was absolute. The rushing water had all but swept it away. The castle was in ruins. The relics of her family, surely lost. The citizens had erected shakey tents on the hill. Most of them had only saved the clothing on their backs when the spirits attacked and had nothing. She would have to lead Arendelle's people as Queen, if they didn't cast her out for her decision at the dam. She had no idea how she would live up to-

She squeezed her eyes shut. Thinking about Elsa risked her knees collapsing beneath her. It had been three days and there were no signs of her sister's return. The Northuldra spiritual leader had told her they believed Elsa to be the 5th spirit of their legend and that she had brought balance back to them all.

_At cost of her life._

It was all Anna could do to keep moving. Arendelle needed her now.

* * *

When Elsa dropped into the icy water below Ahtohallan, her first thought was she needed to get back to Anna. The voice she had been seeking was her own.. somehow. The fifth spirit. The Avatar. Elsa struggled to understand. She had lived before? The people from her dreams were her past lives? As soon as the voice spoke to her and unlocked this new certainty inside of her, everything had gone very cold and very dark. The cold had been unimaginable.

While she drifted in this state she caught glimpses of Anna. Anna had woken the earth spirits and destroyed the dam. Destroyed _Arendelle_ to calm the spirits and right an ancient wrong. She did what Elsa failed to do with all her magic and power... she brought balance back to the spirits. She believed Elsa had _died_. Elsa's heart squeezed. She desperately needed to find Anna and help her through this. And Anna might be the only one who could make sense of what she had found within the glacier. She kicked harder towards the light above her, determined to reach it despite the strong current.

Elsa broke the surface with a gasp.

It was all wrong.

When she caught her breath, she saw she was in a bright, frozen ocean. There were a few floating icebergs, but no sign of the glittering glacier of Ahtohallen. Elsa called out for the Nokk and it didn't show itself either. She was alone.

She pulled herself onto an icy platform and faced the sky. It was clear. The sea was calm, not at all like the dark sea she had crossed. Her heart lurched with questions. There was no way she drifted that far out of the dark sea, right? She tried to call for the Nokk again. Even striking the water with her ice, as if she could command it to appear.

It was odd that the Nokk didnt respond. She had thought it would be waiting on her. Even odder was the calming of the dark sea and that she couldnt see Ahtohallen anymore.

She settled on not worrying about it for now. She only needed to get home. If the spirits had changed something about the world, it would be clear soon enough. Elsa took a moment to consider how wrong she had been to go into Ahtohallen at all. She feels like the last few days happened in a dream, the spirit called to her so strongly she could barely think of anything else but getting there. She had been out of control from the moment she heard the spirit calling her. It was an odd feeling, losing control of your mind in that way. Elsa shivered at the realization that she almost lost Anna for her mistakes. Almost lost herself within the glacier. She has to get back.

She couldn't have gone that far. A glance at the sky showed her the bright sun and she picked the direction she thought was south. She confidently stepped off the iceberg, the touch of her feet freezing the water beneath her.

"No matter, I am Queen Elsa of Arendelle and I can walk to land." Saying it out loud made it real. She tried to shake the feeling of wrongness. She just needed to see Anna and spend the rest of her life apologizing for the worst mistake she had ever made.

* * *

"Aang, this is the worst idea you have ever had," said Sokka, "and you've had some pretty bad ones."

"Just a few more days here. You saw the Fire Nation ships. They know something has changed too." Aang said, "Besides, arent you supposed to be descended from the water tribe? Where's your 'icy constitution' now?"

"Being related to the extinct water tribe doesnt make me immune to the cold! Especially since you keep hogging all the food and wouldnt let me bring any meat. How am I supposed keep going?" said Sokka, laying flat on his back in Appa's saddle.

"If you can hunt us one of those tiger seals down there, I will personally cook and eat it with you. I promise." Aang smiled back at Sokka before focusing his gaze back to the ice. His friend had a point thought. They had been flying Appa over the frozen ocean for three days and seen nothing but penguins, ice, and blue water. He kept scanning the horizon and hoping.

"If we don't miraculously find your Avatar soon, the monks are not going to be happy about our sky bison heist. We can't stay out here forever. I told you all I knew about Ahtohallen from my grandmother and even she never thought it was actually real, just a fantasy for a dead tribe." Sokka continued, "We have to talk about giving this up and trying to beg the monks for forgiveness." Aang wasn't listening anymore, he was looking at a Fire Nation ship far in the distance that wasn't moving. "-we havnt been gone that long. We can just pretend Appa got stuck in a tree and we were saving him-"

"Sokka stop."

"No really, the monks can't prove we went all the way to the south pole with one of the last sky bison-"

"Sokka look at that Fire Nation ship. They never bother to patrol this deep into the ice anymore. What do you see?" Something in Aang's voice got Sokka's attention. He grabbed for the spyglass and aimed it where Aang pointed. Sokka was completely silent for nearly a minute and Aang held his breath the entire time.

"They are fighting someone," he said, voice shaking. "I think its... its a waterbender."

Aang nearly shouted. He pulled Appa around and urged him towards the ship as quickly as possible before grabbing his glider. He hoped they weren't too late.

* * *

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_AN: I hope you all approve of the direction I'm taking. Sorry for short chapter but I didn't need it to be any longer and I just want to set up._

_Elsas bit was the hardest to write. I rewrote it several times entirely. It still might change. Her voice and choices are hard to nail down. Plus writing a clueless dimensionally displaced character is always hard at first heh._

_Question for you: Do you mind me including canon ATLA characters like Aang or would you prefer all OCs?_

_Reviews are my applause. Con-Crit (or just crit heh) welcome. PMs open. Thanks for reading!_


	3. Dont Run Into Fire

Elsa only made it an hour before she noticed a ship in distance. She nearly fell through her own ice in relief. She had felt confident until she started to walk. She wasn't even sure she was still in the Dark Sea at this point. Things were... odd. A ship would at least have navigation equipment, knowledge of the surrounding seas, and could actually help her get home.

She was so happy to see the ship she almost missed the smoke. A pillar of dark smoke rose in the air above the ship, which as she got closer she could now see was massive, black, and seemingly made of metal. She had heard of nothing like this from the castle advisors and she was certain no ships of this build ever visited Arendelle's port. It was even coming right towards her now. She didn't want to assume the worst, but the appearance of the ship put caution into her approach. She considered leaving it alone since it was unlikely to have ever visited Arendelle if she was so unfamiliar with it. And it was rather foreboding, all harsh angles and belching fire.

She deliberated for a while, weighing her options. Ultimately, she decided she would still approach them. She was the Snow Queen and she could protect herself from whatever threat they may pose even if they prove to be hostile in the worst-case scenario. Pirates or a foreign enemy included. Arendelle was famous in this region even before the eternal winter incident and the chances of them knowing of its location or at least the general direction was high. Hopefully they could clear up where she is now, if nothing else.

When it got close enough, she could see people on board in striking red armor. The flame insignia flag it flew was wholly unfamiliar to her. A flick of her wrist and the ice she stood on solidified into a larger, starburst platform. There could be no mistaking who they would be dealing with if they knew anything about this region at all. The Queen of Arendelle was quite intimidating when she wanted to be and had a reputation. The ship was slowing in front of her.

Elsa chose to speak first as soon as they were within earshot. "I am Queen Elsa of Arendelle. I would like to speak to the captain of this ship." She stood tall, her voice ringing out over the ice. She could see the people on the ship squinting down at her with wary expressions. They didn't react to her title except to mutter amongst themselves.

Eventually, a man called out, "We would be delighted to receive you, your ah, majesty. We will send a boat."

"No need." She stepped forward, an icy bridge forming to the deck of the ship. The shocked gasps of the crew weren't unexpected. She only hoped they wouldn't react violently. If so, would leave the same way and escape if things did not go well. Elsa tried to tell herself not to be so paranoid, this was just covering all her options. It was only the smart thing to do. She had lost her head when the spirit called her and she refused to let it happen again.

When her feet touched the deck, she let the bridge dissolve behind her. The crew had schooled their expressions. They were obviously trained soldiers now that she could see them clearly. This was a warship. With a very distinctly flame motif. Elsa narrowed her eyes.

"What kingdom are you from?" She began, noticing the metal ship lacked even a sail to propel itself.

"The real question is where have you been hiding, waterbender?" A man in a more decorated suit of armor said from across the deck. One look at his shining metal hairpiece and medals adorning his uniform indicated this was the captain. Or at least someone in charge.

Waterbender is what he called her. She knew that term only because of the spirit in the glacier and she was shocked to hear it from the captain. She steeled herself. "I am the reagent of Arendelle. Located on the southern fjords. Perhaps you know of me as the Snow Queen."

The captain's lips were tight as he considered her. His arms crossed. "Arendelle." He tasted the word. "And how many other waterbenders are you harboring, Queen Elsa?" His mouth tugged into a smile as he used her title. Elsa didn't like it.

"If you are referring to my ice, I am the only one I have ever met with this ability." Elsa swallowed. "What kingdom are you from, Captain? I didn't catch it the first time." She felt she might need the escape plan after all. The hostility was overwhelming.

"This ship, like all others, is from the Fire Nation," he said as if that explained everything. He was pacing around her. "I have one more question for you. Where is _the Avatar_?"

Elsa couldn't stop her eyes from widening. This was too much to be a coincidence. The captain was grinning widely in front of her now, watching her expression. "I'm afraid I don't know what you mean." She saw him glance over her shoulder and nod infinitesimally to someone. She made to turn back to the railing but was blocked by a ring of soldiers.

"Unfortunately, I can't let you leave," the captain said behind her. "I am under orders directly from the Fire Lord to detain all waterbenders and bring them to him. Especially those I suspect to be the avatar. Bind her."

Elsa didn't wait for the soldiers to move. A quick wave of her hand brought up a thick wall of ice between herself and the soldiers, and swept the five closest to the railing to the side, clearing the path for her easy escape.

"Don't let her off this ship! This has to be the avatar! We need to get her quickly before she can access the avatar state." She heard someone shouting. The men were lining up.

Then, her world changed.

Jets of yellow fire, hot and directed, blasted her ice away in an instant and blocked her escape route. Elsa traced the stream with her eyes and saw it was being produced from the hands of every soldier on the deck. Fire magic. All of them. It was almost a relief to see other people like her, and Elsa felt frozen. Her entire life she had been the only one. But everyone on this ship... they have fire. Then, the first hot jet caught her in the side and she cried out, trance broken. These people were attacking her. She was outnumbered 100 to 1. She could actually _lose._

Elsa whipped into action. The air dropped 40 degrees. Ice covered the feet of every man she could see. She raised her hands and great icy beams gripped the sides of the ship, sending its nose into the air to knock the remaining soldiers off-balance, including the Captain who had somehow already melted his feet free. It didn't work, and they moved fluidly into a martial arts stance she had only seen in paintings from far away before more fire shot from their hands directly towards her.

Her heart lurched. She had only a second to raise an ice wall, feeling like she was back in front of Han's men in her castle. The fire broke through her ice again. It was seemingly explosive in its destruction. She shot a beam towards the captain, hoping to pin him to the deck. He lept to the side like a dancer and dodged easily, sending more fire spinning from his feet this time. Elsa backed up squinting against the heat, throwing more walls up to protect her front. That's when she felt someone grab her from behind.

She was panicking enough that it had begun to snow over the ship, frost creeping over the deck. But the fire users behind her seemed to produce their own heat and had wrested her hands behind her. Their hot touch burned her arms and she was rapidly overpowered. She cried out and tried to pull away, but there were at least three holding her now, keeping her hands immobilized. They had shackles and were just about to click them onto her when a blast of wind knocked them off balance for a moment, and one released their grip on a hand.

She didn't waste a moment and encased them in ice up their chests this time. She made a break for the railing. More men blocked her. Before she could even call her ice, they were swept completely off the side of the ship by another powerful gust of wind.

This time, Elsa saw the source. A young man, a teenager even, covered in blue arrow tattoos was whipping up a windstorm on the deck. He blocked their fire easily with concentrated gusts of unnatural wind that could only be more magic. He was barely touching the ground between each blast. He caught her eyes after he forced another few men over the side with a spin of his staff.

"Avatar! I'm here to help! Just- Iv been looking for you." He was working his way towards her. "I can explain after we get off this ship. I can get you away from the firebenders. You have to trust me."

She pulled more ice up to grip the ship, hearing the metal groan. "Thanks for the rescue." she ground out, "but I just want to get home."

"I have a flying bison! I can take you there, anywhere. Please, just come with me." He was nearly at her side, face all earnest concentration. The whole deck was covered in ice and the captain still stood shooting flames. She was ready to dispute the boy's outlandish claim when a great roar came from above. A shaggy, six-legged creature ridden by a tan-skinned man in a ponytail came from the sky. It had a saddle like a common beast and swept from the sky to hover over the battle. Great balls of fire from the upper deck were already being directed towards it. Elsa forced another swath of ice towards the men firing them.

She was now near enough to the railing now that she could jump into the ocean below and escape. The ice gripping the ship would keep them there long enough she could get a head start. Elsa considered leaving all of them behind. But she realized she still wasn't sure precisely which direction Arendelle was in. The sun was still up and she had little frame of reference. And well.. this kid had risked his own life to free her. Watching him fight the man in front of her she noticed his face was earnest and his strikes were all non-lethal deflections. That decided it for her, in the end.

"Alright, let's go." At the end of the day, he _was_ acting friendly towards her. She had no reason to distrust him and he had a rather convenient method of transportation. Elsa had a horrible feeling she was not anywhere near Arendelle anymore and she wanted desperately to speak to another person, especially another magic user, who knew about this avatar business.

He grinned ear to ear, finally reaching her side. "Hold on!" He grabbed her hand and put one arm around her waist and then a tight blast of air shot them both skyward. She yelped in a very undignified way and had only a moment to feel the weightlessness before they both landed in the saddle of the beast. "Sokka, get us out of here," the boy called.

"Holy shit Aang you actually got her! And look at this fire nation ship, that's a LOT of ice, they won't be moving for a while." Sokka said. The flying bison rapidly gained altitude, zig-zagging through the sky above the ship. She could still see the ship, completely lifted from the water by her massive pillars. The water surrounding the ship was frozen entirely for a hundred paces out. She allowed herself to feel a bit of pride.

"I know!" The boy cut him off, deflecting another fireball. "It was close. They had her nearly in cuffs." They were already so high the attacks were sparse. She thinks they were almost out of range.

"Well, at least the monks won't kill us now. They can't punish us if we bring them the _avatar._"

Elsa's mind finally caught up with what they were talking about. "I am not going anywhere except Arendelle. You will take me _there_, not to any monks." She interjected, with as much queenly majesty as was possible sitting cross-legged in the saddle of the beast. "And will someone please explain this Avatar business to me?"

* * *

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_AN: yall have no idea how many edits this went through and I'm still not fully happy._

_Why did Elsa lose so quickly? She isn't a trained fighter. Her powers are OP but these are a ship full of benders who spend their whole life learning how to fight other benders. Elsa panicked, isn't that physically strong, and never fought someone with powers. plus she wasn't prepared to butcher them all with ice to the heart or something._

_Question of the day- Do you think Elsa should have beaten them? Or gone on the ship at all?_

_Criticism welcome- I want to improve my writing and this fic. Comments are my applause. Don't forget to follow._


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